Device for forming shear keyways on sides of extruded slabs and the like

ABSTRACT

An endless belt with projections on the outer surface is mounted on the side plates of a concrete slab making machine so that as the slab is formed, horizontal shear keyways are formed in the sides of the slab. When adjacent slabs are grouted, the keyways and the grout form horizontal shear key assemblies which prevent horizontal and vertical movement from occurring from between slabs.

United States Patent Herbert et al.

[ 1 Dec. 25, 1973 DEVICE FOR FORMING SHEAR KEYWAYS 0N SIDES 01F EXTRUDED SLABS AND THE LHKE Inventors: Denys Herbert; Ernst Martens, both of Winnipeg, Manitoba, Canada Assignee: Spiroll Corporation Ltd., Winnipeg,

Manitoba, Canada Filed: June 22, 1972 Appl. No.: 265,150

Foreign Application Priority Data July 2, 1971 Great Britain 31,221/71 US. C1 425/329, 425/64, 425/371, 425/187 C Int. Cl. B29g 2/02 Field of Search 425/64, 114, 218, 425/233, 237, 329, 336, 367, 370, 371, 4 C, 817 C [56] References Cited UNITED STATES PATENTS 2,395,920 3/1946 Grotenhuis 425/329 X 2,670,515 3/1954 3,201,845 8/1965 3,284,867 11/1966 3,561,050 2/1971 Danforth 425/367 X Primary Examiner-H. A. Kilby, Jr. Att0rneyStanley G. Ade

[ 5 7 ABSTRACT An endless belt with projections on the outer surface is mounted on the side plates of a concrete slab making machine so that as the slab is formed, horizontal shear keyways are formed in the sides of the slab. When adjacent slabs are grouted, the keyways and the grout form horizontal shear key assemblies which prevent horizontal and vertical movement from occurring from between slabs.

33 Claims, 11 Drawing Figures PATENTEB DEC 2 5 I375 SHEET 1 UP 3 PATENTEB HERE 5 I975 SHEET 2 OF 3 DEVICE FOR FORMING SHEAR KEYWAYS ON SIDES OF EXTRUDEI) SLAIBS AND THE LIKE BACKGROUND OF THE INVENTION This invention relates to new and useful improvements in shear keyway forming devices for longitudinally extending concrete slabs normally used for floor and ceiling construction.

Such slabs can be manufactured by a variety of machines but preferably they are extruded behind a machine which moves along a pair of rails, the slab being formed upon a bed with the machine being moved along the rails by the extruding process.

Such slabs are normally formed with a plurality of longitudinally extending apertures therethrough and, when manufactured, longitudinally extending grooves are formed in the sides of the slab which act as vertical shear keyways. When the slabs are erected, the space between adjacent slabs and the longitudinal keyways are filled with a grout which prevents vertical movement occurring between adjacent slabs.

However, it is also desirable and in fact necessary in many locations, to prevent horizontal relative movement between adjacent slabs and normally steel plates are embedded at the ends of the slabs and are then welded together. However, this is not satisfactory and is time consuming apart from the difficulty of obtaining access to the plates for the welding process. I

SUMMARY OF THE INVENTION The present invention overcomes these disadvantages by providing shear keyways in the sides of the slabs as they are being formed by the machine which, when grouted, prevent horizontal movement from oc curring between adjacent slabs.

Another object of the invention is to provide a device of the character herewithin described which is driven by the relative movement between the machine and the slab being formed. Alternatively, and in some types of slab making machines, the device can be power driven.

A yet further object of the invention is to provide a device of the character herewithin described which includes means to adjust the angle of inclination to the vertical of the keyway forming projections.

A further object of the invention in conjunction with the last mentioned object is to provide a device of the character herewithin described in which the angle of inclination of the inner run of the belt can be adjusted relative to the longitudinal axis of the machine so that the best angle of entry of the projections can be set.

Still another object of the invention is to provide a device of the character herewithin described which is easily fitted to existing slabmaking machines.

Another object of the invention is to provide a device of the character herewithin described which is simple in construction, economical in manufacture and otherwise well suited to the purpose for which it is designed.

With the foregoing objects in view, and such other or further purposes, advantages or novel features as may become apparent from consideration of this disclosure and specification, the present invention consists of the inventive concept which is comprised, embodied, embraced, or included in the means, method, process, product, construction, composition, arrangement of parts, or new use of any of the foregoing, herein exemplified in one or more specific embodiments of such concept, reference being had to the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric, partially schematic view of the device attached to a concrete slab forming machine.

FIG. 2 is an enlarged isometric view of the device attached to the side plate of the machine with the machine removed for clarity and showing a portion of the slab formed with the shear keyways formed thereon.

FIG. 3 is a sectional view of two adjacent slabs showing the relationship of the shear keyways.

FIG. 4 is a top plan view of the device shown in relation to one of the forming augers of the machine and showing an alternative shape of the belt used in forming the shear keyways.

FIG. 5 is an isometric view of the preferred embodiment of the belt.

FIG. 6 is a cross sectional view along the line 6-6 of FIG. 4.

FIG. 7 is a side elevation of one of the belt pulleys showing means to drive the belt.

FIG. 8 is a cross sectional view of one embodiment of the belt.

FIG. 9 is a cross sectional view of a second embodiment of the belt.

FIG. 10 is a cross sectional view of a third embodiment of the belt.

FIG. 111 is a schematic front elevation of a portion of the belt showing various shapes of shear keyway forming projections.

In the drawings like characters of reference indicate corresponding parts in the different figures.

DETAILED DESCRIPTION Proceeding therefore to describe the invention in detail, referenceto FIG. 1 will show a concrete slab forming machine collectively designated 10 and including a pair of spaced and parallel rails I 1 upon which the machine is mounted by means of wheels 12. A hopper I3 is provided within which concrete is placed and it is compacted within a packing chamber generally in the area indicated by reference character 14. It is extruded rearwardly upon a pallet (not illustrated) and the machine moves in the direction of arrow 15 being pushed along by the concrete slabs to being formed by the machine. Such a machine is exemplified in U. S. Pat. No. 3,284,867.

The device collectively designated 17 is situated upon each side of the machine (only one being shown in the drawings) upon side plates 11% of the packing or compaction chamber situated in the area 14.

The side plate 18 is provided with a longitudinally extending aperture 19 and an angulated bracket 20 is secured to one end of the side plate and to the frame of the machine (not illustrated).

The device 17 includes a frame generally indicated by 21 which includes a pair of spaced and parallel horizontally disposed plates 22 (see FIG. 6), an outer longitudinally extending belt guide 23 and an inner combination attaching plate and belt guide 24 all of which may be welded together or otherwise secured.

Trailing and leading belt guide means 25 are provided and take the form of forks 26 having a central tongue 27 extending therefrom. The forks 26 are provided with pulleys 27 journalled upon spindles 2%, ball races 29 mounting the pulleys for rotation in a horizontal plane.

The tongue 27 slides between the aforementioned upper and lower plates 22 and bolts 30 normally clamp the tongues between the plates 22 as clearly shown in FIG. 2. However, an adjusting bolt 31 screw threadably engages the rear end of the tongue and reacts between a cross bar 32 spanning the inner and outer guides 23 and 24, so that rotation of this adjusting bolt, once the clamp bolts 30 have been slackened, moves the forks inwardly or outwardly relative to one another. These bolts act as belt adjustors to adjust the tension in the belt collectively designated 33 and which engages around the pulleys 27.

The device is attached to the side plates 18 over the longitudinal apertures 19, by means of a plurality of screw threaded bolts 34 screw threadably engaging the side plates. FIG. 2 shows the uppermost of these bolts whereas FIG. 6 shows the upper and lower bolts.

Set screws or studs 35 screw threadably engage through the inner attaching plate and guide 24 and abutt against the side plate. This means that the position of the device can be varied within limits relative to the concrete slab forming machine. FIG. 6 shows the bolts adjusted to adjust the angle of the device vertically with the underside being closer to the side plate than the upper side thereof.

FIG. 4 shows the bolts and studs have been used to adjust the longitudinal axis 36 of the devicerelative to the longitudinal axis 37 of the machine, it being understood that the auger 38 lies parallel to the longitudinal axis of the machine.

In the latter case, the belt 33 has been adjusted so that the leading end 39 of the inner run 33A is substantially flush with the inner surface 40 of the side plate and the trailing end 41 of the inner run 33A projects inwardly of the inner surface of the side plate, the reasons for which will hereinafter become apparent.

The outer surface of the belt is provided with a plurality of shear keyway forming projections 41 which may take various shapes and configurations as shown in the drawings.

The preferred embodiment is illustrated in FIGS. 1 and with the projections being substantially rectangular when viewed in side elevation. However, the upper sides 42 slope downwardly and outwardly from the main web 43 of the belt and the lower sides 44 slope upwardly and outwardly relative thereto but not to the same degree. The leading side surface 45 may be substantially at right angles to the web 43 but the trailing side surface 46 slopes slightly inwardly from the web towards the outer vertical face 47 of the projections.

In operation, the angle of inclination is set by the set screws 35 and the attaching bolts 34 so that the device is situated, for example, as shown in FIGS. 4 and 6.

As the slab 16 is formed by the machine, the machine moves in the direction of arrow and the projections on the inner run 33A of the belt form the shear keys 48 in the sides 49 of the slab as clearly shown in FIGS. 2 and 3.

When used with an auger type machine as illustrated in FIG. 4, the tapered auger 38 compresses the concrete in the area 50 between the auger and the side plate 40 and the engagement of the projections with this concrete as it is being formed, rotates the belt around the pulleys in the direction of arrow 51 thus gradually forming the shear keyways to the maximum depth at the trailing end 40 of the belt.

The configuration described relative to the belt shown in FIG. 5 facilitates the clean withdrawal of the projections from the finished keyways 48 as the belt moves around the trailing pulley specifically designated 27A. The angle of inclination of the device when viewed in plan as in FIG. 4, gradually forms the keyways and in conjunction with the concrete being compressed, also assists in compressing the areas surrounding the shear keyways 48.

The angle of inclination illustrated in FIG. 6 enables the device to form keyways 48 having a base deeper than the upper side as shown in FIG. 3.

Formed conventionally by the concrete slab forming machine, is the longitudinally extending shear keyway 52 and this is situated above the keyways 48. These keyways 48 extend from the adjacent the lower boundary of the keyway 52 to the underside of the slab or may terminate spaced from the underside as illustrated in FIG. 2.

Various configurations of belt projections may be utilized although the embodiment shown in FIG. 2 is preferred. FIG. 4 shows a belt having the projections 41A in the form of counter curves with the side profile being similar to that illustrated in FIG. 8.

Alternatively the profile can be as illustrated in FIGS. 9 or 10.

FIG. 11 shows a variety of different shape projections it being understood, of course, that the preferred shape only would be used on a belt. Reference character 418 shows a foursided triangular projection. 41C illustrates a square projection. 41D illustrates a truncated foursided cone shaped projection. 41E illustrates a semispherical projection. 41F illustrates a truncated conical projection and 41 G illustrates a rectangular shaped projection. However, other shapes, of course, may be used as desired.

When the shear keyways have been formed, adjacent slabs are placed together as illustrated in FIG. 3 and the area 53 between the slabs is filled with grout 54. The longitudinally extending shear keyways 52 prevent vertical movement between the two slabs and the shear keyways 48 prevent longitudinal movement between the slabs as well as assiting the longitudinal shear keyways 53 in maintaining the vertical alignment between the slabs.

When used in an extrusion machine illustrated in FIG. 1, it is normally not necessary to provide any drive for the belt which can free wheel around the pulleys, the rotative movement being provided by the relative movement between the machine and the slab being formed thereby.

However, when used with some machines, it may be desirable to provide a source of power for the belt and FIG. 7 shows one method of providing this power. An hydraulic motor 55 is connected to a source of hydraulic pressure (not illustrated) and is connected to the spindle 28 of one of the pulleys 27. This rotates the pulley at the same time rotating the belt but, of course it will be appreciated that it is absolutely essential that the linear speed of the inner run of the belt be exactly the same as the linear speed of the relative movement between the machine and the slab and in this connection a conventional slip clutch assembly shown schematically in FIG. 7 by reference character 56, may be provided.

The angle of inclination both vertically and horizontally of the device relative to the machine may be adjusted to give the best formation of the shear keys 48 and the clean withdrawal of the projections therefrom at the trailing end of the device.

in this regard, the location of the device relative to the auger assembly 38 is of the utmost importance. The auger assembly includes a tapered auger shaft 38A increasing in diameter from the leading end 388 towards the trailing end 38C. The auger flight 38D has a constant diameter so that the depth of the auger flight relative to the tapered shaft 38A gradually decreases from a maximum at the leading end 3813 to zero at the trailing end 38C. A trowelling mandrel 38E is formed beyond the termination of the auger flight 38D by an extension of the full diameter portion of the shaft 38A.

It has been found that the leading end 39B of the belt preferably should be located adjacent to the second spiral 38F of the tapered auger flight 38D so that the shear keyways 48 commence to be formed as the con crete reaches the critical stage of compaction.

It will, of course be appreciated that the concrete starts to compact at the end 38B of the auger flight and reaches full compaction at the opposite end 38C. With the device set at an angle to the longitudinal axis 37 of the machine, the shear keyways are gradually formed as the concrete reaches its maximum compaction due to the funnelling or throating relationship between the tapered auger and the inner run of the belt. This means that as the projections on the inner run reach the trailing end of the inner run, the shear keyways 48 are fully formed in fully compressed or compacted concrete and they then withdraw cleanly from the keyways as this portion of the belt moves around the trailing pulley 27.

Finally reference to FIG. 6 will show that longitudinally extending recesses 23' and 24 are formed on the outer surfaces of the outer and inner side plates 23 and 24 respectively, to receive and guide the web 43 of the belt 33 and to support same vertically.

Various modifications may be constructed or performed within the scope of the inventive concept dis closed. Therefore what has been set forth is intended to illustrate such concept and is not for the purpose of limiting projection to any herein particularly described embodiment thereof.

What we claim as our invention is:

1. In a concrete slab forming machine which includes a packing chamber having a pair of opposed longitudinally apertured side plates; a horizontal shear keyway forming device, means for mounting said device one upon each side plate at said longitudinal apertures, said device including a frame, belt guide means at each end of said frame and an endless belt extending around said belt guide means whereby the inner run of the belt engages through said aperture in the side plate and engages the side of the concrete slab being formed by the machine, and a plurality of outwardly extending shear keyway forming projections on the outer surface of said belt.

2. The device according to claim l in which said belt guide means takes the form of a pair of pulleys journalled for rotation one at each end of said frame and in a horizontal plane.

3. The device according to claim l which includes front and rear side guide means for said belt on said frame and being situated longitudinally between said belt guide means.

4. The device according to claim 2 which includes front and rear side guide mans for said belt on said frame and being situated longitudinally between said pulleys.

5. The device according to claim 1 in which said means mounting said device upon said side plate includes further means to adjust the angle of inclination of the inner run of said belt from the vertical and said further means also adjusting the angle of inclination of the inner run of said belt relative to the longitudinal axis of the machine thereby controlling the degree of penetration of the projections into the side of the concrete slab.

6. The device according to claim 2 in which said means mounting said device upon said side plate includes further means to adjust the angle of inclination of the inner run of said belt from the vertical and said further means also adjusting the angle of inclination of the inner run of said belt relative to the longitudinal axis of the machine thereby controlling the degree of penetration of the projections into the side of the concrete slab.

7. The device according to claim 3 in which said means mounting said device upon said side plate in cludes further means to adjust the angle of inclination of the inner run of said belt from the vertical and said further means also adjusting the angle of inclination of the inner nm of said belt relative to the longitudinal axis of the machine thereby controlling the degree of penetration of the projections into the side of the concrete slab.

8. The device according to claim 4 in which said means mounting said device upon said side plate includes further means to adjust the angle of inclination of the inner run of said belt from the vertical and said further means also adjusting the angle of inclination of the inner run of said belt relative to the longitudinal axis of the machine thereby controlling the degree of penetration of the projections into the side of the concrete slab. I

9. The device according to claim 1 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.

it). The device according to claim 2 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.

111. The device according to claim 3 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.

12. The device according to claim 4- in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.

13. The device according to claim 5 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.

14. The device according to claim 6 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.

15. The device according to claim 7 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.

16. The device according to claim 8 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.

17. The device according to claim 2 which includes means to adjust the tension in said belt, said means including a slide plate for mounting each of said pulleys in said frame, and a screw threaded adjusting bolt reacting between said frame and said slide plates for moving same endwise relative to said frame and clamp bolt means for clamping said slide plates onto said frame when adjusted.

18. The device according to claim 4 which includes means to adjust the tension in said belt, said means including a slide plate for mounting each of said pulleys in said frame, and a screw threaded adjusting bolt reacting between said frame and said slide plates for moving same enwise relative to said frame and clamp bolt means for clamping said slide plates onto said frame when adjusted.

19. The device according to claim 6 which includes means to adjust the tension in said belt, said means including a slide plate for mounting each of said pulleys in said frame, and a screw threaded adjusting bolt reacting between said frame and said slide plates for moving same endwise relative to said frame and clamp bolt means for clamping said slide plates onto said frame when adjusted.

20. The device according to claim 10 which includes means to adjust the tension in said belt, said means including a slide plate for mounting each of said pulleys in said frame, and a screw threaded adjusting bolt reacting between said frame and said slide plates for moving same endwise relative to said frame and clamp bolt means for clamping said slide plates onto said frame when adjusted.

21. The device according to claim 2 which includes means to drive said belt, said last means including a source of power operatively connected to one of said pulleys and slip clutch means between said source of power and said pulley whereby the linear speeds of said slab being formed and said belt are the same.

22. The device according to claim 4 which includes means to drive said belt, said last means including a source of power operatively connected to one of said pulleys and slip clutch means between said source of power and said pulley whereby the linear speeds of said slab being formed and said belt are the same.

23. The device according to claim 6 which includes means to drive said belt, said last means including a source of power operatively connected to one of said pulleys and slip clutch means between said source of power and said pulley whereby the linear speeds of said slab being formed and said belt are the same.

24. The device according to claim 10 which includes means to drive said belt, said last means including a source of power operatively connected to one of said pulleys and slip clutch means between said source of power and said pulley whereby the linear speeds of said slab being formed and said belt are the same.

25. The device according to claim 17 which includes means to drive said belt, said last means including a source of power operatively connected to one of said pulleys and slip clutch means between said source of power and said pulley whereby the linear speeds of said slab being formed and said belt are the same.

26. The device according to claim 18 which includes means to drive said belt, said last means including a source of power operatively connected to one of said pulleys and slip clutch means between said source of power and said pulley whereby the linear speeds of said slab being formed and said belt are the same.

27. The device according to claim 19 which includes means to drive said belt, said last means including a source of power operatively connected to one of said pulleys and slip clutch means between said source of power and said pulley whereby the linear speeds of said slab being formed and said belt are the same.

28. The device according to claim 20 which includes means to drive, said belt, said last means including a source of power operatively connected to one of said pulleys and slip clutch means between said source of power and said pulley whereby the linear speeds of said slab being formed and said belt are the same.

29. A concrete slab forming machine comprising in combination with a source of power, a hopper, a packing chamber having a pair of opposed longitudinally apertured side plates, and at least one auger assembly extending therein, said auger assembly including a shaft portion and an auger flight extending therearound, said shaft portion increasing in diameter from the leading end to the trailing end, the outer diameter of said auger flight remaining constant whereby the depth of said auger flight gradually diminishes from a maximum at said leading end to zero at the trailing end, a horizontal shear keyway forming device, means for mounting said device one upon each side plate at said longitudinal apertures, said device including a frame, belt guide means at each end of said frame and an endless belt extending around said belt guide means whereby the inner run of the belt engages through said aperture in the side plate and engages the side of the concrete slab being formed by the machine, and a plurality of outwardly extending shear keyway forming projections on the outer surface of said belt.

30. The device according to claim 29 in which said belt guide means takes the form of a pair of pulleys joumalled for rotation one at each end of said frame and in a horizontal plane.

31. The device according to claim 29 in which said means mounting said device upon said side plate includes further means to adjust the angle of inclination of the inner run of said belt from the vertical and said further means also adjusting the angle of inclination of the inner run of said belt relative to the longitudinal axis of the machine thereby controlling the degree of penetration of the projections into the side of the concrete slab.

32. The device according to claim 29 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.

33. The device according to claim 29 which includes means to adjust the tension in said belt, said means including a slide plate for mounting each of said pulleys in said frame, and a screw threaded adjusting bolt reacting between said frame and said slide plates for moving same endwise relative to said frame and clamp bolt means for clamping said slide plates onto said frame when adjusted. 

1. In a concrete slab forming machine which includes a packing chamber having a pair of opposed longitudinally apertured side plates; a horizontal shear keyway forming device, means for mounting said device one upon each side plate at said longitudinal apertures, said device including a frame, belt guide means at each end of said frame and an endless belt extending around said belt guide means whereby the inner run of the belt engages through said aperture in the side plate and engages the side of the concrete slab being formed by the machine, and a plurality of outwardly extending shear keyway forming projections on the outer surface of said belt.
 2. The device according to claim 1 in which said belt guide means takes the form of a pair of pulleys journalled for rotation one at each end of said frame and in a horizontal plane.
 3. The device according to claim 1 which includes front and rear side guide means for said belt on said frame and being situated longitudinally between said belt guide means.
 4. The device according to claim 2 which includes front and rear side guide mans for said belt on said frame and being situated longitudinally between said pulleys.
 5. The device according to claim 1 in which said means mounting said device upon said side plate includes further means to adjust the angle of inclination of the inner run of said belt from the vertical and said further means also adjusting the angle of inclination of the inner run of said belt relative to the longitudinal axis of the machine thereby controlling the degree of penetration of the projections into the side of the concrete slab.
 6. The device according to claim 2 in which said means mounting said device upon said side plate includes further means to adjust the angle of inclination of the inner run of said belt from the vertical and said further means also adjusting the angle of inclination of the inner run of said belt relative to the longitudinal axis of the machine thereby controlling the degree of penetration of the projections into the side of the concrete slab.
 7. The device according to claim 3 in which said means mounting said device upon said side plate includes further means to adjust the angle of inclination of the inner run of said belt from the vertical and said further means also adjusting the angle of inclination of the inner run of said belt relative to the longitudinal axis of the machine thereby controlling the degree of penetration of the projections into the side of the concrete slab.
 8. The device according to claim 4 in which said means mounting said device upon said side plate includes further means to adjust the angle of inclination of the inner run of said belt from the vertical and said further means also adjusting the angle of inclination of the inner run of said belt relative to the longitudinal axis of the machine thereby controlling the degree of penetration of the projections into the side of the concrete slab.
 9. The device according to claim 1 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.
 10. The device according to claim 2 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.
 11. The device according to claim 3 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.
 12. The device according to claim 4 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.
 13. The device according to claim 5 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.
 14. The device according to claim 6 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.
 15. The device according to claim 7 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.
 16. The device according to claim 8 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.
 17. The device according to claim 2 which includes means to adjust the tension in said belt, said means including a slide plate for mounting each of said pulleys in said frame, and a screw threaded adjusting bolt reacting between said frame and said slide plates for moving same endwise relative to said frame and clamp bolt means for clamping said slide plates onto said frame when adjusted.
 18. The device according to claim 4 which includes means to adjust the tension in said belt, said means including a slide plate for mounting each of said pulleys in said frame, and a screw threaded adjusting bolt reacting between said frame and said slide plates for moving same enwise relative to said frame and clamp bolt means for clamping said slide plates onto said frame when adjusted.
 19. The device according to claim 6 which includes means to adjust the tension in said belt, said means including a slide plate for mounting each of said pulleys in said frame, and a screw threaded adjusting bolt reacting between said frame and said slide plates for moving same endwise relative to said frame and clamp bolt means for clamping said slide plates onto said frame when adjusted.
 20. The device according to claim 10 which includes means to adjust the tension in said belt, said means including a slide plate for mounting each of said pulleys in said frame, and a screw threaded adjusting bolt reacting between said frame and said slide plates for moving same endwise relative to said frame and clamp bolt means for clamping said slide plates onto said frame when adjusted.
 21. The device according to claim 2 which includes means to drive said belt, said last means including a source of power operatively connected to one of said pulleys and slip clutch means between said source of power and said pulley whereby the linear speeds of said slab being formed and said belt are the same.
 22. The device according to claim 4 which includes means to drive said belt, said last means including a source of power operatively connected to one of said pulleys and slip clutch means between said source of power and said pulley whereby the linear speeds of said slab being formed and said belt are the same.
 23. The device according to claim 6 which includes means to drive said belt, said last means including a source of power operatively connected to one of said pulleys and slip clutch means between said source of power and said pulley whereby the Linear speeds of said slab being formed and said belt are the same.
 24. The device according to claim 10 which includes means to drive said belt, said last means including a source of power operatively connected to one of said pulleys and slip clutch means between said source of power and said pulley whereby the linear speeds of said slab being formed and said belt are the same.
 25. The device according to claim 17 which includes means to drive said belt, said last means including a source of power operatively connected to one of said pulleys and slip clutch means between said source of power and said pulley whereby the linear speeds of said slab being formed and said belt are the same.
 26. The device according to claim 18 which includes means to drive said belt, said last means including a source of power operatively connected to one of said pulleys and slip clutch means between said source of power and said pulley whereby the linear speeds of said slab being formed and said belt are the same.
 27. The device according to claim 19 which includes means to drive said belt, said last means including a source of power operatively connected to one of said pulleys and slip clutch means between said source of power and said pulley whereby the linear speeds of said slab being formed and said belt are the same.
 28. The device according to claim 20 which includes means to drive, said belt, said last means including a source of power operatively connected to one of said pulleys and slip clutch means between said source of power and said pulley whereby the linear speeds of said slab being formed and said belt are the same.
 29. A concrete slab forming machine comprising in combination with a source of power, a hopper, a packing chamber having a pair of opposed longitudinally apertured side plates, and at least one auger assembly extending therein, said auger assembly including a shaft portion and an auger flight extending therearound, said shaft portion increasing in diameter from the leading end to the trailing end, the outer diameter of said auger flight remaining constant whereby the depth of said auger flight gradually diminishes from a maximum at said leading end to zero at the trailing end, a horizontal shear keyway forming device, means for mounting said device one upon each side plate at said longitudinal apertures, said device including a frame, belt guide means at each end of said frame and an endless belt extending around said belt guide means whereby the inner run of the belt engages through said aperture in the side plate and engages the side of the concrete slab being formed by the machine, and a plurality of outwardly extending shear keyway forming projections on the outer surface of said belt.
 30. The device according to claim 29 in which said belt guide means takes the form of a pair of pulleys journalled for rotation one at each end of said frame and in a horizontal plane.
 31. The device according to claim 29 in which said means mounting said device upon said side plate includes further means to adjust the angle of inclination of the inner run of said belt from the vertical and said further means also adjusting the angle of inclination of the inner run of said belt relative to the longitudinal axis of the machine thereby controlling the degree of penetration of the projections into the side of the concrete slab.
 32. The device according to claim 29 in which said projections have a height less than the thickness of the slab being formed and being positioned upon said side plate whereby the upper side of said projections is below the upper side of said slab being formed.
 33. The device according to claim 29 which includes means to adjust the tension in said belt, said means including a slide plate for mounting each of said pulleys in said frame, and a screw threaded adjusting bolt reacting between said frame and said slide plates for moving same endwise relative to said frame and clamp bolt means for clamping said slide plates onto said frame when adjusted. 